The field of the disclosure relates generally to gas turbine engines and, more particularly, to systems and apparatus for surface coolers in a gas turbine engine.
At least some known gas turbine engines include one or more oil cooling systems that are configured to cool and lubricate components of gas turbine engines. Some gas turbine engines include an air-oil surface cooler, or heat exchanger, attached to, for example, surfaces of an aircraft, such as the nacelle, or outer surfaces of the gas turbine engine. Such air-oil surface coolers use fan air and/or external air to cool the oil flowing through the air-oil surface cooler. Known air-oil surface coolers include rigid fins that protrude into a bypass airflow passageway of the gas turbine engine. The rigid fins facilitate transferring heat from the heated oil to the relatively cool fan air.
Some known air-oil surface coolers, however, are inefficient due to the use of rigid materials. For example, in some known gas turbine engines, the cooling fluid flow angle changes direction based in part on the operating conditions of the gas turbine engine. The rigid materials used in known air-oil surface coolers have a fixed and rigid geometry, which facilitates generating pressure loses and friction losses to the changing flow angle of the cooling fluid flowing through the bypass airflow passageway, which reduces the fuel efficiency of the engine.
In addition, some known air-oil surface coolers are sized to remove a predetermined amount of heat from the oil. However, known gas turbine engines operate at a range of engine speeds. For example, at a ground/idle state, fan air flows through the nacelle at a reduced flow rate, and at a steady state cruising condition, fan air flows through the nacelle at an increased flow rate. Thus, to remove the predetermined amount of heat at reduced fan air flow rates, known air-oil surface coolers have an increased size and thus weight, as opposed to that which would be needed at increased fan air flow rates. The increased size of the air-oil surface coolers facilitates increased friction losses when exposed to the increased fan air flow rates.